The invention relates to a friction surface member for an open-end friction spinning arrangement, having yarn forming surface portions that are provided with air passage openings, and to a process for manufacturing this type of friction surface member.
It is shown in German Unexamined Patent Application DE-OS No. 31 14 093 to provide the surface of a roller for a friction spinning arrangement with a coating. The coating has the purpose of making possible an advantageous friction value or coefficient of friction with respect to the fibers. It consists of a ceramic material, preferably chromium dioxide, which is applied by means of a plasma coating process. The coating in this case also takes place in the area of the outside mouths of the air passage openings, so that these receive a rounded edge.
In the case of rollers for open-end friction spinning arrangements, the air passage openings are used to cause fiber transport by means of a pneumatic flow, and to hold the fibers in the area of the yarn forming zone. However, sometimes these air passage openings interfere with the actual sequence of the spinning process. For reasons concerning manufacturing technology and also to provide sufficiently high air throughput, it is not possible to make the air passage openings very small. Therefore, during the feeding as well as during the spinning, fibers are frequently pulled into the air passage openings by the ends or by other areas. These fibers are held in these openings increasingly so that, as a result, the perfect tying-up of the fibers into the forming yarn is impaired. With a surface treatment, it was found that this effect is further increased when an increased friction effect is generated. Therefore, as a result, the effect that is produced by the increase of the friction effect which is advantageous for the spinning per se, is further impaired.
An object of the invention is to provide a friction surface member having a yarn forming surface that produces an improved tying-up of the fibers into the forming yarn.
This object is achieved by providing at least a portion of areas surrounding air passage openings with a section having a surface that has a different coefficient of friction value than the remaining area of the yarn forming surface. In certain preferred embodiments, the portion of areas surrounding the air passage openings have a section with a lower coefficient of friction value than the remaining areas of the yarn forming surface.
This development makes it possible that, on the one hand, the friction value can be selected and increased in such a way that the yarn to be spun receives an advantageous twist. On the other hand, however, the danger of fibers being pulled into the air passage openings and held fast is reduced a comparable degree such that when the present invention is used, the fibers are pulled out of the air passage openings relatively easily, without impairing the spinning process. Therefore, there is no increased resistance to the pulling-out of the fibers from the edges of the mouth.
According to advantageous features of certain preferred embodiments of the invention, it is provided that the outer mouth areas of the air passage openings have surfaces that are made of the same material as the remaining areas of the outer shell surface, but are subjected to a different surface treatment. As a result, it becomes possible in a relatively easy way to obtain the endeavored distribution of the friction values. In a further development of the invention, it is advantageous to structure the yarn forming surface outside the outer mouth areas by a surface treatment. In certain preferred embodiments, the structuring may take place, for example, by means of electrical discharge machining or laser radiation which results in miniature crater-type depressions in the surface.
According to advantageous features of certain preferred embodiments of the invention, it is provided that the outer shell surface and the outer mouth areas of the air passage openings are coated with a hard material that forms a smooth surface, and that the outer shell surface, outside the outer mouth areas, is provided with a subsequently worked-in surface structure. A hard coating of this type helps prevent early wear of the rollers. Further, during the structuring of the surface, particularly by means of electrical discharge machining or laser radiation, miniature crater-type depressions are formed in the hard coating which have edge areas without a warped (bell-mouthed) shape.
According to advantageous features of certain preferred embodiments of the invention, it is provided that the outer mouth edges of the air passage openings are rounded off before a coating is applied. This ensures that after the coating, the mouth edges maintain a defined shape that is not accidental. This defined shape is also advantageous for pulling-off of fibers projecting into the air passage openings.
According to advantageous features of certain preferred embodiments of the invention, it is provided that the shell surface of the roller in a yarn withdrawal direction is divided into two or several sections having a different coefficient of friction values. As a result, it becomes possible to take spinning conditions into account. Particularly in the area of the forming yarn tip, a smaller twist is introduced than in the area that follows where the yarn has a larger diameter.
According to certain advantageous features of certain preferred embodiments of the invention, a process is provided for forming the unique friction surface member.
According to advantageous features of certain preferred embodiments of the invention, the process provided includes:
(a) forming air passage openings into a shell of a roller; PA0 (b) grinding an outer shell surface of the shell to a cylindrical shape; PA0 (c) rounding off the outer mouth areas of the air passage openings; PA0 (d) coating the outer shell surface, and outer mouth areas with a material; PA0 (e) placing radial bearings in the roller; PA0 (f) grinding the coating on the roller to a cylindrical shape while said roller is being held by said radial bearings; PA0 (g) providing a rougher surface only to said outer shell surface.
By means of this process, a roller can be obtained that has an advantageous distribution of coefficient of friction values, has very precisely treated surfaces, and particularly has very good concentricity because the final cylindrical grinding takes place when the roller is already held in its operational radial bearings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.